Abstract: Accurate estimation of evaporation rate in bare soil is of great significance for hydrogeological processes in arid regions. Potential evaporation has been regard as a standard to estimate the actual evaporation rate. In applications, evaporation rate in the saturated bare soil (PE_s) is often replaced by water evaporation rate (PE_w). Whether this simplification is adequate needs to be verified. This research is based on the measured potential evaporation rates (by lysimeters) and meteorological elements. The results show that PE_s is higher than PE_w on a yearly scale, and the differences are more obvious especially in spring and summer. In summer, PE_s is greater than PE_w at day but smaller at night. Besides, the curve of PE_w lags behind PE_s. Detailed analyses of evaporation dynamics over fully saturated bare sandy soils and water surface are provided by energy balance considerations. PE dynamics are mainly governed by available energy (R_n−G_s/N_w). Compared with water, the existence of solid particles in the saturated bare soil results in a smaller albedo and heat capacity, which has a further influence on R_n and G_s. Available energy for the saturated bare sandy soil is higher than that of water (R_n,s−​​​​​​​G_s>R_n,w−​​​​​​​​​​​​​​N_w), resulting in a higher rate for PE_s. The peak value of G_s exists earlier than N_w, leading to lag of PE_w behind PE_s. This research provides a theoretical basis for accurate calculation of the actual evaporation rate and groundwater resources.